Apparatus and method for gas-liquid separation

ABSTRACT

A two phase gas-liquid separation apparatus is provided that shapes the flow in a flow shaping line. Shaping the two-phase flow allows centrifugal force to send the heavier, denser liquid to the outside wall of the flow shaping line and allows the lighter, less dense vapor or gas to occupy the inner wall of the flow shaping line. With the gas positioned on the inner wall of the flow shaping line, an exit port on the inner wall will allow for the majority, if not all, of the gas, along with a low amount of liquid, to be sent to a conventional separator. A high ratio of vapor/liquid at a flow rate much lower than the total flow rate within the flow shaping line is sent to the conventional separator. This allows for efficient separation of the vapor from the liquid with the use of a smaller conventional separator.

FIELD OF THE INVENTION

The present invention generally relates to the separation of gas from agas-liquid two phase flow stream. More specifically, it relates todirectionally shaping the gas-liquid two phase flow stream so that themajority of the gas is located in a certain area of the flow stream,which allows effective separation of the gas and the liquid.

BACKGROUND OF THE INVENTION

A gas-liquid two phase flow stream includes a mixture of differentfluids having different phases, such as air and water, steam and water,or oil and natural gas. A gas-liquid two phase flow takes many differentforms and may be classified into various types of gas distributionwithin the liquid. These classifications are commonly called flowregimes or flow patterns and are illustrated in FIGS. 1A-1E. Bubble flowas illustrated in FIG. 1A is typically a continuous distribution ofliquid with a fairly even dispersion of bubbles in the liquid. Slug orplug flow as illustrated in FIG. 1B is a transition from bubble flowwhere the bubbles have coalesced into larger bubbles with a sizeapproaching the diameter of the tube. Churn flow as illustrated in FIG.1C is a pattern where the slug flow bubbles have connected to oneanother. In annular flow as illustrated in FIG. 1D, liquid flows on thewall of the tube as a film and the gas flows along the center of thetube. Finally, in wispy annular flow as illustrated in FIG. 1E, as theliquid flow rate is increased, the concentration of drops in the gascore increases, leading to the formation of large lumps or streaks ofliquid.

It is often desirable to separate the gas and liquid components of afluid from one another to enable proper operation of systems, such ascertain types of liquid pumps. Conventional vertical or horizontalgas-liquid separators are available to separate gas from liquid.Conventional separators typically employ mechanical structures, whereinan incoming fluid strikes a diverting baffle which initiates primaryseparation between the gas and liquid components. Mesh pads or demisterpads are then used to further remove suspended liquid. The sizing of aseparator and the particular characteristics of the separator isdependent upon many factors, which may include, the flow rate of theliquid, the liquid density, the vapor density, the vapor velocity, andinlet pressure. Vertical separators are typically selected when thevapor/liquid ratio is high or the total flow rate is low. Horizontalseparators are typically preferred for low vapor/liquid ratio or forlarge volumes of total fluid.

One application of these types of separators is in oil and gas drillingoperations. Specifically, a mud-gas separator is used when a kick isexperienced in a wellbore during drilling operations. A kick is the flowof formation fluids into the wellbore during drilling operations. If akick is not quickly controlled, it can lead to a blow out. As part ofthe process for controlling a kick, the blow-out preventors areactivated to close the wellbore and wellbore fluids are slowlycirculated out of the wellbore while heavier drilling fluids are pumpedinto the wellbore. A mud gas separator is used to separate natural gasfrom drilling fluid as the wellbore fluid is circulated out of thewellbore. Often times, however, prior act separators, including mud-gasseparators, cannot keep up with the flow rate from the wellbore.

Of course, separators are also used in the production of oil and gas toseparate natural gas out of the oil that is being produced.Additionally, there are many other applications that require the use ofgas-liquid separators.

SUMMARY OF THE INVENTION

This invention relates to directionally shaping two-phase mixed flow ina curved path within a flow shaping line prior to introduction into aseparator so as to enhance operation of the separator. Shaping thetwo-phase flow in a curvilinear path will allow centrifugal force tomore readily force the heavier, denser liquid to the outside wall of theflow shaping line in the curved path and allow the lighter, less densevapor or gas to occupy the inner wall of the flow shaping line. Once thegas is fairly well positioned on the inner wall of the flow shapingline, an exit port located on the inner wall will allow for themajority, if not all, of the gas, along with a low amount of liquid, tobe sent to a conventional separator. A very high ratio of vapor/liquidat a flow rate much lower than the total flow rate within the flowshaping line is then sent to the conventional separator. This allows forefficient separation of the vapor from the liquid with the use of asmaller, more economical conventional separator than what would havebeen required for the full flow rate.

Additionally, a fluid guiding surface may be placed on the inner wall ofthe flow shaping line at the exit port to further aid in directing thegas to flow to the conventional separator. Furthermore, the liquidreturn from the conventional separator may be arranged in closedownstream proximity to the exit port on the inner wall of the flowshaping line. The close proximity of the liquid return and the exit portallows the use of a venturi, nozzle or other restriction locatedadjacent the liquid return in the flow shaping line just downstream ofthe exit port. The venturi, nozzle or other restriction accelerates thevelocity of the liquid in flow shaping line as it flows across the exitport. This acceleration of the liquid helps to pull the liquid out ofthe conventional gas-liquid separator. In addition, the acceleration ofthe liquid within the flow shaping line helps to prevent any solids thatmay be present in the gas-liquid flow from entering the exit port and ithelps to lower the amount of liquid that enters the exit port and thusenters the conventional separator.

The invention therefore allows a gas-liquid fluid to be effectivelyseparated with the use of a smaller conventional separator than waspreviously possible. The invention accomplishes this without usingadditional complex mechanical devices and thus will operate efficientlyand reliably.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present disclosure and advantagesthereof may be acquired by referring to the following description takenin conjunction with the accompanying figures, wherein:

FIGS. 1A-1E illustrate a cross-sectional view of various flow regimes oftwo phase gas-liquid flow.

FIG. 2 illustrates a cross-sectional view of an embodiment of separationapparatus.

FIG. 3 illustrates a cross-sectional view of the embodiment of theseparation apparatus in FIG. 2 taken across line 3-3.

FIG. 4 illustrates a cross-sectional view of another embodiment of aseparation apparatus with two flow shaping loops.

FIG. 5 illustrates a cross-sectional view of another embodiment of aseparation apparatus where the diameter of the flow shaping line is lessthan the diameter of the main line.

FIG. 6 illustrates a cross-sectional view of another embodiment of aseparation apparatus where the flow shaping line forms a generallyelliptical shape.

FIG. 7 illustrates a cross-sectional view of another embodiment of aseparation apparatus with two exit ports.

FIG. 8 illustrates a cross-sectional view of another embodiment of anexit port in a separation apparatus.

FIG. 9 illustrates a cross-sectional view of another embodiment of anexit port with an airfoil shape located away from the inner wall in anembodiment of a separation apparatus.

FIG. 10 illustrates a cross-sectional view of another embodiment of aseparation apparatus located near the seabed in an oil and gas drillingoperation.

DETAILED DESCRIPTION

In the detailed description of the invention, like numerals are employedto designate like parts throughout. Various items of equipment, such aspipes, valves, pumps, fasteners, fittings, etc., may be omitted tosimplify the description. However, those skilled in the art will realizethat such conventional equipment can be employed as desired.

FIG. 2 illustrates a cross-sectional view of an embodiment of aseparation apparatus 10. In an exemplary embodiment, the separationapparatus 10 includes a gas-liquid flow 12 traveling in a verticaldirection 14 in a main line 15. The gas-liquid flow 12 could be any typeof multiphase gas-liquid flow regime or flow pattern, such as, forexample, bubble flow, slug or plug flow, churn flow, annular flow orwispy annular flow. The gas-liquid flow 12 within main line 15 isdirected into a circular flow path 16 in a flow shaping line 17. Thecircular flow path 16 of flow shaping line 17 creates an increaseddistribution of the gas on inner wall 24 of the flow shaping line 17.The increased distribution of the gas on the inner wall 24 of the flowshaping line 17 results in part by the relatively heavier and denserliquid 18 of flow 12 being forced to the outer wall 20 of the flowshaping line 17 due to centrifugal force of circular flow path 16, whilethe lighter gas 22 is driven to the inner wall 24. In an embodiment witha vertical or partly vertical orientation of the flow shaping line 17,gravitational effects may also aid in increasing the distribution of thegas on the inner wall 24 of the flow shaping line 17. In an embodiment,a transition section 13 between the main line 15 and flow shaping line17 may be provided with a shape as illustrated to further aid increating the increased distribution of the gas on inner wall 24 of theflow shaping line 17.

As the gas-liquid flow 12 continues to travel through the circular flowpath 16 of flow shaping line 17, the gas-liquid flow 12 forms a flowpath that exhibits a high concentration of the gas 22 on the inner wall24 of the flow shaping line 17. In the embodiment shown in FIG. 2, atlocation 26, which is approximately 315 degrees around shaping line 17(or 45 degrees from the vertical), the separation of gas 22 from liquid18 has reached a degree that gas 22 primarily occupies the spaceadjacent the inner wall 24 of the flow shaping line 17. As seen in FIG.3, which is a cross section 3-3 of the flow shaping line 17 andgas-liquid flow 12 at location 26, the gas 22 occupies mainly the innerwall 24 of the circular flow path 16 of the flow shaping line 17.

With gas-liquid flow 12 forming a more stratified flow regime, or atleast the distribution or volume of gas near the inner wall 24 of theflow shaping line 17 has increased at the point of location 26, the gas22 may now be effectively bled off from the gas-liquid flow 12 at anoutlet port 28 positioned on the inner wall 24 of the flow shaping line17. Although outlet port 28 may be positioned any where along flow path16, it is preferably selected to be at a point where substantialseparation of gas from liquid has occurred. Thus, in one preferredembodiment, the outlet port 28 is downstream of location 26. At about alocation 26, which is approximately at an angle of approximately 45degrees from the vertical 74, it has been found that the concentration,separation or stratification of the gas 22 from the liquid 18 is at apoint that gas 22 occupies a greater volume of space adjacent the innerwall 24 of the main line 15 than liquid 18. In other embodiments, theoutlet port 28 may be located between generally 45 degrees from thevertical and generally zero degrees with the vertical. While location 26is illustrated at approximately 315 degrees around flow shaping line 17and has been found to be a point where a substantial volume of gas hasbeen driven to inner wall 24, location 26 is used for illustrativepurposes only.

In an exemplary embodiment, a fluid guiding surface 30 is located on theinside diameter 32 of the inner wall 24 of the flow shaping line 17upstream of the outlet port 28. The fluid guiding surface 30 includes adownstream end 36 that curves around the corner 37 located at thejunction of the outlet port 28 and the flow shaping line 17. In oneembodiment, the fluid guiding surface 30 may comprise at least a partialairfoil or hydrofoil shape. The fluid guiding surface 30 functions toguide the gas 22 into the outlet port 28. The gas 22 follows the contourof the fluid guiding surface 30 and the gas 22 will follow the curve ofthe downstream end 36 into the outlet port 28.

An amount of liquid 18 from the gas-liquid flow 12 will also be carriedinto the outlet port 28 thus forming a new gas-liquid flow 40 whichincludes a much lower percentage of liquid compared to the gas-liquidflow 12. The new gas-liquid flow 40 from outlet port 28 is then directedinto a conventional gas-liquid separator 38, as shown in FIG. 2, forfurther separation of the gas and liquid. Outlet port 28 is connected tothe conventional gas-liquid separator by separator inlet line 33. Thegas-liquid separator 38 contains a gas exit 39 to allow for the removalof the gas 22 separated from the new gas-liquid flow 40. The gas-liquidseparator 38 also contains a liquid exit 41 that is connected to liquidinlet port 42 in a return line 43 by a separator liquid exit line 44.The return line 43 is formed at the end of, and is fluidicly connectedto, the flow shaping line 17. Those skilled in the art will appreciatethat separation apparatus 10 is shown as integrated with gas liquidseparator 38, but can be a completely separate structure.

In an exemplary embodiment, the liquid inlet port 42 in the return line43 is in close downstream proximity to outlet port 28 of the flowshaping line 17. The close proximity of the liquid inlet port 42 and theoutlet port 28 allows the use of a venturi 46 located adjacent theliquid inlet port 42 in the return line 43. The venturi 46 acceleratesthe velocity of the liquid 18 in return line 43 as it flows across theliquid inlet port 42. This acceleration of liquid 18 helps to draw theliquid out of the conventional gas-liquid separator 38. In addition, theacceleration of the liquid 18 within return line 43 facilitatesseparation of gas from liquid within flow shaping line 17, minimizes thelikelihood that any solids present in the gas-liquid flow 12 will enteroutlet port 28, and minimizes the amount of liquid 18 that enters theoutlet port 28.

It has been observed that the liquid flow rate entering the outlet port28 in the new gas-liquid flow 40 is approximately twenty percent of theof the flow rate of the gas-liquid flow 12 that is in the flow shapingline 17 upstream of the outlet port 28. The new gas liquid flow 40contains a higher percentage of the gas 22 than was in the gas-liquidflow 12, but with much lower amount of liquid 18 in the flow. Thisprovides a very efficient first step in the separation of the gas 22from the liquid 18 without the use of additional pumps, valves or othermechanical equipment.

This efficient first step in the separation of the gas 22 from theliquid 18 is provided at least in part by one or more aspects of theinvention. First, the use of the circular flow path 16 to centrifugallyincrease the concentration of the gas 22 on the inner wall 24 of theflow shaping line 17. Second is the fluid guiding surface 30 used todirect the gas 22 into the outlet port 28. Third, venturi 46 acceleratesthe velocity of the liquid 18 as it flows past the outlet port 28,thereby functioning to lower the amount of liquid 18 that enters theoutlet port 28 and minimize entry of solids into outlet port 28. Theventuri 46 also lowers the pressure of the liquid 18 at the liquid inletport 42 of the return line 43, which draws the liquid 18 out of theconventional gas-liquid separator 38.

As mentioned above, the efficient first step in the separation of thegas 22 from the liquid 18 significantly decreases the amount of liquid18 entering the conventional gas-liquid separator 38. This allows forthe use of much smaller size conventional gas-liquid separators thanwould have previously been possible for a given flow rate.

While circular flow path 16 is shown as positioned in a vertical plane,in another embodiment the circular flow path 16 could be in a horizontalplane or in a plane with an inclination between horizontal and vertical.

In another embodiment, illustrated in FIG. 4, the circular flow path 16could be replicated in multiple loops 78 to develop the increasedconcentration of the gas 22 on the inner wall 24 of the flow shapingline 17. In another embodiment as seen in FIG. 5, the flow shaping line17 may be formed with a smaller cross-sectional area 72 than the crosssectional area 70 of the main line, thereby increasing the velocity ofthe gas-liquid flow 12 within the flow shaping line 17. The increase invelocity of the gas-liquid flow 12 results in greater centrifugal forceand increased concentration of the gas 22 on the inner wall 24 of theflow shaping line 17. A higher velocity through the flow shaping line 17also allows for greater turndown capability in the flow rate of thegas-liquid 12 in a system where the flow rate may be variable.

In other embodiments, as illustrated in FIG. 6, the flow pattern couldbe elliptical 80, or partially circular or partially elliptical, or someother curvilinear, non-circular shape that would still provide forincreased concentration of the gas 22 on the inner wall 24 of the flowshaping line 17 through the use of centrifugal force.

As seen in FIG. 7, other embodiments of the invention may employmultiple outlet ports 28. For example, in one embodiment, an outlet port28 may extend from the approximate bottom of a first loop, similar tothe embodiment of FIG. 2, but the pipe may continue to make a secondloop similar to the embodiment of FIG. 4, and have a similarly situatedsecond outlet port 28 at the approximate bottom of the second loop. Inaddition, in another embodiment, one or more conventional separators maybe used.

Other embodiments of the invention may eliminate the fluid guidingsurface 30 or utilize other structures. For example, as illustrated inFIG. 8, in one embodiment, an outlet port 28 may have a curved entrance82. In another embodiment illustrated in FIG. 9, a fluid guiding surface84 could be spaced away from the inner wall 24 of the flow shaping line.In addition, other embodiments of the invention may use a nozzle orother type of restriction in lieu of a venturi to accelerate the fluidflow across the outlet port 28 or across the liquid inlet port 42, ormay use no restriction at all.

As described above, one application for the invention is to protectagainst “kicks,” such as in subsea applications, by circulating outhydrocarbon gas at the seabed floor before the gas is able to rise up toa drilling rig. Referring to FIG. 10, in an exemplary embodiment,illustrated is a conventional sub-sea blow out preventer 50 located onthe seafloor 52. A marine riser 54 extends from the blow out preventer50 and within the riser is a drillpipe 56. An embodiment of theseparation apparatus 10 is positioned along drillpipe 56, preferablyadjacent the blow out preventer 50. In normal drilling operations,drilling fluid 58 is pumped down the drillpipe 56 from the drilling rig(not shown) and returns to the drilling rig via annulus 60 formedbetween the drillpipe 56 and the riser 54. If a “kick” is detected, forexample, by a change in the level of the mud tanks or increase in mudcirculation rate, inlet annulus valve 62 is activated, divertingdrilling fluid 58 from annulus 60 into the flow shaping line 17. Naturalgas 64 entrained in drilling fluid 58 from the “kick” is then separatedfrom the drilling fluid 58 by the separation apparatus 10 as describedabove. The natural gas 64 exits the gas-liquid separator 38 at the gasexit 39 and may flow up riser 66 to the drilling rig where it may besafely handled, for example, sent to a flare boom of the drilling rig(not shown), or compressed and re-distributed (also not shown).

Following separation of natural gas 64 from the drilling fluid 58 byseparation apparatus 10, the drilling fluid 58 is re-introduced into theannulus 60 at an exit annulus valve 68. In comparison with the usualprocedure of handling a kick, the use of an embodiment of this inventionallows for full flow or circulation of the drilling fluid without havingto choke down the flow or operate the blow out preventer valves.

In another embodiment, the inlet annulus valves 62 or exit annulusvalves 68 can be eliminated, bypassed or operated so that the upwardflowing drilling fluid 58 continually flows through the separationapparatus 10. Compared to the usual procedure on a drilling rig whenthere is a kick of choking the flow of the drilling fluid and being ableto only send a portion of the flow to the mud-gas separator located onthe drilling rig, an embodiment of the present invention allows the fullflow of the drilling fluid to be handled by the separation apparatus 10and the separation safely takes place near the seafloor.

The foregoing invention allows the use of a separation apparatus thatcan efficiently separate gas from a gas-liquid flow and do so at highflow rates and with the use of smaller conventional separators thanwould otherwise be possible at the high flow rates.

It is therefore evident that the particular illustrative embodimentsdisclosed above may be altered or modified and all such variations areconsidered within the scope and spirit of the present invention. Also,the terms in the claims have their plain, ordinary meaning unlessotherwise explicitly and clearly defined by the patentee.

Although illustrative embodiments of the invention have been shown anddescribed, a wide range of modification, changes and substitution iscontemplated in the foregoing disclosure. In some instances, somefeatures of the present invention may be employed without acorresponding use of the other features. Accordingly, it is appropriatethat the appended claims be construed broadly and in a manner consistentwith the scope of the invention.

1. An apparatus for separating gas from liquid in a gas-liquid flow, said apparatus comprising: a first pipe having a first end and a second end, wherein at least a portion of the pipe between said first end and second end is curvilinear in shape so as to be characterized by an inner wall and an outer wall at said curvilinear portion of said pipe; an outlet port disposed in said pipe along the inner wall between said first and second ends; a gas separator in fluid communication with the outlet port.
 2. The apparatus of claim 1, further comprising a fluid guiding surface formed on the inner wall of the pipe adjacent said outlet port.
 3. The apparatus of claim 1, further comprising a foil disposed in said pipe adjacent said outlet port.
 4. The apparatus of claim 1, further comprising a restriction formed in the pipe between said outlet port and said second end.
 5. The apparatus of claim 4, wherein said restriction is adjacent said outlet port.
 6. The apparatus of claim 4, wherein said restriction is a nozzle.
 7. The apparatus of claim 1, wherein a substantially all of the pipe between said first end and the outlet port is curvilinear.
 9. The apparatus of claim 1, said pipe having a liquid inlet disposed therein between said outlet port and said second end, said gas separator comprising a liquid return line, wherein said liquid return line is in fluid communication with said liquid inlet of said pipe.
 10. The apparatus of claim 9, further comprising a restriction formed in the pipe between said outlet port and said liquid inlet.
 11. The apparatus of claim 10, wherein said restriction is adjacent said liquid inlet.
 12. The apparatus of claim 11, wherein said restriction is a nozzle.
 13. The apparatus of claim 7, wherein said curvilinear pipe forms a circle around an axis, wherein said outlet port is disposed in said inner wall at a point between approximately 315 and 360 degrees around said axis.
 14. The apparatus of claim 1 further comprising a second pipe having a first end and a second end, wherein at least a portion of the second pipe between said first end and second end is curvilinear so as to be characterized by an inner wall and an outer wall at said curvilinear portion of said pipe, wherein the second end of the first pipe is in fluid communication with the first end of the second pipe.
 15. The apparatus of claim 1, further comprising at least two outlet ports disposed in said pipe along the inner wall between said first and second ends, wherein each outlet port is in fluid communication with said gas separator.
 16. A method for separating gas from liquid in a gas-liquid flow, said method comprising: directing a gas-liquid flow into a curvilinear flow path; concentrating gas within a first portion of said flow path; concentrating liquid within a second portion of said flow path; separating said first portion of said flow path from said second portion of said flow path; and directing said first portion of said flow path into a gas separator.
 17. The method of claim 16, further comprising the step of combining liquid from said gas separator with said second portion of said flow path down stream of the separation point of said flow paths.
 18. The method of claim 16, wherein said first portion of said flow path is characterized by a first radius around a central axis and said second portion of said flow path is characterized by a second radius around said central axis, wherein said second radius is larger than said first radius.
 19. The method of claim 17, further comprising the step of increasing the velocity of said second portion of said flow path after separation from said first portion but prior to the step of combining liquid from said gas separator.
 20. The method of claim 16, further comprising the step of altering the cross-sectional diameter of said flow path to alter the velocity of said gas-liquid flow.
 21. The method of claim 16, wherein said curvilinear flow path is substantially circular.
 22. The method of claim 7, wherein said curvilinear shape is substantially circular.
 23. The method of claim 7, wherein said curvilinear shape is oval. 